Telephone-exchange system



Feb. 23 1926.

R. s BAILEY TELEPHONE EXCEANGE SYSTEM Filed NOV. 12. 1923 2 Sheets-Sheet 1 IN VENTOR E. ifiza'ley A TTORNE Y Feb. 23 1926.

- R. s. BAILEY TELEPHONE momma SYSTEM 2 Sheets-Sheet 2 Filed Nov. 12. 1923 IN VEN TOR 1B Jifim'ley ATTORNEY To all whom it may concern:

Patented Feb. 23, 1926.

UNITED STATES earner @FFICE.

RAND S. BAILEY, OF MONTCLAIR, NEW JERSEY, ASSIG-NOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A'CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed November 12, 1923. Serial No. 674,301.

Be it. known that I, RAND S.

' residing at Montclair, in the county of Essex and State of New Jersey, have invented certain Improvements in Telephone Exchange Systems, of which the following isa specification.

This invention relates to telephone exchange systems, and more particularly to fcircuit arrangements for use at private ybranch exchanges.

An object of the invention is to provide an improved circult vfor use at aprivate branch exchange to interconnect subscribers represents a trunk which extends from a extensions of the private branch exchange and to connect the subscribers extensions or the private branch exchange with trunk lines leading to a main central office.

A feature of the invention consists in providing a circuit arrangement Ior this purpose which is of a simple and cilicicntcharacte" and which requires only a munniuin amount of apparatus for its operation. F or a more complete understanding of the invention, reference may be had to the accompanying drawings in which Figures 1 and 2 illustrate embodiments of the in vention applied to a private branch es:- change. r

Referring to Fig. l or the drawings, T

private branch exchange to a main central otlice and which is provided with supervisory and holding equipment. T and T representadditional trunks similar to trunk T but with said supervisory and holding equipment eliminated. Keys K are provided for the purpose of connecting the atitendants telephone set with the trunks, and additional keys which are serially connected with each other and associated with each trunk are also provided for connecting the subscribers extensions with said trunks. These keys when thrown to a ringing position are. also adapted to signal the subscribers connected with the extensions individually, and a master key MK is also provided for signaling any of the extensions. In Fig. 2, T represents a trunk extending from a private branch exchange to the main central ofiice and K the key by which the private branch exchange attendant may connect the telephone set with said trunk. Additional trunks or transmission circuits BAILEY,

tension.

- transmitted over the tip and ring conductors of trunk T from the main central ollice thereby energizing relay 5. The operation otrelay 5 closes a circuit through the lower winding of relay 6 thereby bridging the latter relayacross the trunk causing itto operate in an obvious manner. The operation 01" relay 6 closes a locking circuit from battery, conductor 7, upper winding and make contacts of relay 6, filament of lamp 8, grounded back contact of supervisory relay 9,. thus lighting the trunk lamp 8. The attendant at the private branch exchange, upon observing the trunk signal 8, actuates key K, thereby bridgingthe attendants set across the tip and ring conductors of the trunk T, causing the operation of supervisory relay 9. The operation of relay 9 opens the locking circuit previously described in connection with relay (5, causing it to be released and the trunk lamp 8 er;- tinguished The attendant, upon connecting the telephone set with the trunk T and learning the number of the desired extension from the operator at the main central oliice restores keyv K thereby releasing relay 9, and actuates a key associated with such ex In this instance it will be assumed that the desired extension is connected to the leads L and that keys K and K are operated. The operation of key K connects the talking conductors leading to the em tension with the tip and ring conductors of trunk T. The operation of key K? to a ringing position causes ringing current to be impressed on the conductors of the extension to signal the subscriber over the following circuit: From ground and source ct current, conductors 10, make contacts of key K conductors L through the signal at the subscribefis extension. In response to the signal the subscriber removes the receiver from its hook and conversesvviththe party at the main central ofiioe- When the re- This serves as a signal to the attendant that the subscriberwhas terminated the call; and

that "the key K may be restored to normal.

The restoration or said key extinguishes' lamp 11'. I

A master key such as is indicatedat MK for ringing any subscribers extension at the private branch exchange may be provided L is desired the operation of key MK closes a circuit from ground and 'battery over conductors 10, .make contacts otJkeyMK, conductors12 and 13, outer inakecontacts 'o fkeys' K "and K these keys being operated at this time, through normal contacts of keys Ktand K overthe conductors L leading, to the subscribers extension and through the polarized ringer, thus signaling the "subscriber' in the. customary manner.

7 1' "The initiation of a call by a subscriber I atone of the extensions causes'the illumination of the lamp associated with that'eX- tension. For instance,-if the calling eX-f {tension is connected with the conductors If, the removal of the receiver from the *s'witclfhool: at that extension closesa 'circuit from,battery',1conductor .7, filament of lamp 11',"*right-hand normal contact of key K grounded left-hand normal contact of said key, normal contacts or keys K and K conductors L through the switch hook at the" extension; In response to thelighting of; lamp 11,. the. attendant operates keys MK 7' and K to a listeningpositionthereby connecting the attendant and subscriber, talkingbattery for such connection being turnished" over the'following path-i battery, upper winding of relay 14, contact 15 of key MK, conductor 16, attendants telephone receiver, contact 17 of dial 18,. attendants i switch hook and transmitter, conductors 19 and 13, make contact 20 ofkey MK, contacts 21 and 22'ofkevK conductors L through 5 ;subscriberstelephone, contacts 23 and 24:

of key-K contact25 of key MK, conductor 12, contact26 of key MK, conductor 2'4", contact 28, lower winding of relay 14Yto ground.

- Thesubscriber informs the atte ndant'of the number desired and restores the receiver atthe extension to its hook itbeing assumed "that the call is for. a connection with the main central office. The attendant, upon learning the number of the desired conn'ec tion restores keys K and" MK and operates the key associated with the idle trunk, for

through supervision is provided, and supervisory relay 9 is operated over; the talk- ,in g conductors of the trunk and..connected iextens'on. hen the extension subscriber. instead of key K which, is used for ringing individual;extensions. Assuming extension formerly" outlined.

instance key K. The operation or this key .bridgesthe 'attendants; telephone set across with the leads L fthereby ringing. the subs scriberas formerly outlined; Whenthe extension is connected with the central otlice hangs upthe receiver, the supervisory; relay 9 releases andcauses the illumination of, lamp, ll as'a disconnect signal over acirc uit The attendant upon noting the lighting of "this, lamp restores key K causingthe circuit to return to nor-- If upon operatingkey--MK- and K? to a talking position it is found theconnection desired istorl another subscriber at the. same private'bran'chexchange, for instance, a sub- .scriber connected withleadsL ant restores key-MK to normal and operates the attendkey K to aringing position thereby-come pleting a circuit from ground and source of current supply, conductors 10, lower make contacts ofkey K9, conductors L through thepolarizedfringer'at the extension. The 00 attendant after ringing on extension L restores key K to a talking position so that the conductors L are bridged across the talking conductors through contacts 29 'and V 30 of key K as is also conductors L through contacts 21 .andf2 1 of key K The subscribers are thus connected with eachother, talkmg current being supplied from .battery and groundthrough the windings of relay 1a and the innernor nal make contacts of key MK to saidtalking conductors. The connectlon of battery and ground through thewindings of relay 14!,in the manner indicated, causes its energization during the perlo'd or conversationbetween the subers to their hooks, at which time the lamps 11, 111 associated "respectively with the extensions L and L will light as disconnect signals over. the following circuit 2' from battery, conductor 7, filame nt ot lamp 11., right-hand normal contacts of keys K and K inner right-hand-make contact of key K conductor 31 to grounded armature or scribers, and until both restore their receivrelay 1 t. The circuit for lighting lamp 111- continues from conducton 7, through fila- -ment-of said lamp, right hand normal contacts of keys K and K, right-hand inner make contact of kcyf K to grou nd over conductor 31. The. attendant, upon noting the illumination of lamps 11 and 111 operates 7 keys K and K to their normal position and the circuit is restored to normal.

The key MK may be also used to signal the called subscriber at the private branch exchange over the path previously outlined. In such instance, however, the key of the subscriber at the calling extension must be "or" relay 33 closes a circuit through its make a contact and left-hand winding of relay 341,

which bridges the latter relay across the talking conductors of the trunk and causes its operation. The operation of relay 3 L closes alockingcircuit through its winding and make contact from battery, filament of lamp 32, rightnormal contact of key K back contact of relay 35, conductor 36 to grounded contact of key 37, thereby lighting lamp 352. p

The attendant, in response to the lighting of lamp 32, operates key l3? and breaks the circuit just described for lighting lamp 32, causing it to be extinguished. The operaftion of key K also bridges the attendants telephone set across the tip and ring conductors of trunk T through contacts 38 and 39 V of said key and through the inner contacts of keys K and K permitting the attendant to converse With the main central oiiice.

Assuming the'call is for connection with an extension such as that terminating in conductors L the attendant operates key K causing the ringing current to be trans mitted from source of current, make contact 40 of said key, over conductors L through the customarypolarized ringer at the subscribers extension to grounded make contact 4 1. The attendant restores key K after ringing the called extension and operates key K Which is associated with the incoming trunk T connecting the subscribers extension set to the tip and ring conductors of said trunk through the make couiacts of key K and the normal contacts of keys K and K, thus permitting the sub scriber connected with the leads L to talk over the trunk T wvitli the main central oii'ice. Upon the termination of the conyersation, when the receiyer at the extension has been returned to its hook, lamp 42 lights as a disconnect signal whereupon the attendant restores K and the circuit returns to normal.

'l'ei t-hand Winding oi relay Upon the initiation of a call from one of the subscribers extensions, the removal of the receirer from its hook causes the illumination of the line lamp associated with that extension. For instance, it the subscriber connected with leads L originates a call, a circuit is established from battery, conduc tor 43, lamp 42, normal contacts of key K the left-hand contact being grounded, inner normal contacts of keys if, it and K through the subscribers station in the usual manner. The attendant Will respond to such signal by operating a key associated with one of the local paths, for instance K and also the attendant key associated with the same path, such as key K". The operation of key K closes a circuit from battery, I id, and from grounded contact oi key K right-hand Winding of relay "is, outer make contacts of key K back contacts of relay as, normal contacts of key K normal contacts 17 and t8 of relay 46, inner normal contacts of key K" over leads L" through the subscribers set at the extension. The closing of this circuit causes'the energixation of relay 14, which, upon operating, completes a locking circuit from its grounded armature and right-hand Winding, and from battery through its left-hand Winding through the contacts of k ys K and K as just outlined; The operation of key K through its grounded le'tt make contact also closes a circuit through the right-hand wind ing of relay li and over the same path. The operation of ke K through its inner make contacts connects the attendants set through the inner normal contacts o't key K to the talking conductors at the C};- tension. If the subscriber, utter being connected with the attendant in the manner indicated, informs the latter that a connection is desired with another extension at the private branch etchange, for instance, an or;- tensiou connected with leads U, the attendantdepresses the ringing key K. j with that extension, ringing current being supplied from source of current, conductor it-9, inner make contact of key K over leads L through the ringer at the called extension to grounded inner let'thand make contact of key K. The operation of key K also closes a circuit from grounded lower .Wiuding oi resistance coil, outer lett make contact oil said key, conductor 50, winding of relay 51, iuncr right make contact of key K and right normal contact of key K, filament of lamp l2, conductor -13, to battery. The closure of this circuit causes the operation of relay 51 which provides a locking circuit through its winding and grounded armature to battery through filament of lamp d2, as just described. Thc'lamp however, is in series with relay 51, and will not light under this condition. Lamp "will belighted dimly as a busy signal during this period over a circuit from gro'undand non-inductive resistance, conductor 53, outer right make contact of relay 51, right normal contacts of keys K and K, filament vof lamp -52, conductor 48 to batt-ery. After a suitable ringing interval liey'K is restored,

and ringing current is'd connected. The operation of relay 51 connects extensionsL and L to each other through the outer make contacts of key K over talking'conductors train 55, outer make contacts of relay 51,

normal I contacts or heysK land K over vthe talking conductors L battery and ground being furnished over this path through the windings-of relayed. Atthe termination or the conversation, when both;

subscribers return the receivers toitheir hooks, the locking circuit 'previouslydescribed'in connection with'i-elay 4% becomes broken causing this relay to release. It the a calling extension abandons-the call and the f 7 receiver thereat is hung up, relay ei' will be "also released? and will not reoperate the subscriber J attempts to originate another call until key K is rcoperated. The releaseio'f J relay 44 causes the illumination of'linc lamp 4:2 as a disconnect signal over a circuit ex-" tending from grounded armature of relay 4t',"rig'ht inner make contact of key K right normal contact of key K filament of lamp42, conductor t to battery. The re lease ofrelay ee'sliort circuits relay 51 causing its 'deenergization which, in turn, extinguisheslamp 52. I ,a p hen the attendant is "talking on a local: transmission path, a separate source ofbattery' supply "is introduced for her set, as for instancevthrough relay bridged" across the path as indicated at cause arelay associated with that path, such as relay 44: to op'erate. The relay 44 will 58, so that she will not therefore operate only when there is an extension bridged across "the local path. This" provision is made 'to prevent operating any of the transmission path connecting relays "suchas relays 4510i 51' associated with the extensions oiih'alf connections'between the "attendant and the-extensions. These relays are protected I from operating falselyv in the 7 following manner :Operating ground is con: nected to allsaid relays associated with aparticular extension line Whenever the individual ringing key-of that line is depressed.

When the connecting transmission paths are" idle, theba-ttery side of the windings ofthe saidf r'elays are also grounded on the back contacts of the associated battery supply,

such relay's'as relay 4A, in the'connect-ing paths, an'dthe path conn'ectingrelays canf'not operate. Then the connecting transmission paths are busy on established conne' cti'0n's, the'battery side ofthe windings ofthe, path connecting relays will also be grounded, this time through an operated low resistance Fpath coi'in-ecting r h T .lish aconnect-ion, the first extension to be *rung will be-connected to the path. As prey iously described, the operating transmission path is through the lamp of the calling subscriber, thepathconn'ecting relay and as? -sociated,non-inductive resistance and ringing keyof thevcalled subscribed. The path connecting "relay, when, operating, short circuits the associated; non-inductive resistance' and; being low Wound, providesa suttransinission-path is justbeing used to estab r ,iiciently low resistance to ground onthe path 7 signalinglejad, so that the[.depresLsion: 07f 'ther ringing: keys will not "causetheassociated path connecting relays to operate from thebatte yof the original calling lines.

The battery supply relay; associated with each, transmission path Willrelease when the telephones of two connected extensions have been replaced on the switchah'ooks and, upon releasing. cannotbe. reoperated'. except'by subsequent operation of theattendantslistening key; 1 This feature, which is, inie'itect,

an instantaneous disconnect, is -introduced here to prevent the battery supply relay from reoperating after'the original connection has been released at the path connecting relay. If the-battery supplyrelay were allowed to reoperate, then the next extension called bythe attendant would be connected with the original calling line in error Although the path connecting relays associated Withtwo connected extensions are grounded at their-respective extension-ringing key,,the proper relayrwill operate since it will b'efthe only one to-havebattery on the batteryside of its winding. V F a 1 What is claimed is 1. In a' private branch exchange compris ing'a plurality of subscribers extensions,z-a

plurality of transmission circuits 'forEinten connecting said extensions, switching means associated Wlllli'QiLGll transmission circuit at each extension for connecting a' calling extensionand transmission circuit, a ringing:

its

tension, and means responsive to the operationrof said ringing key/for automatically connecting the called extension to the transmission circ uit connected with a calling ex tension. i

3. In a' telephone systenrcomprising a main central oflice and branch exchange, a I

plurality of subscribers extensions at the branch exchange, a plurality of trunk lines for interconnecting the subscribers extensions and main central office, a plurality of transmission circuits local to the branch exchange for interconnecting the subscribers extensions, keys associated With said trunk lines and transmission circuits in serial relation with each other for connecting the calling extensions with the trunk lines and transmission circuits, means associated With said extensions for impressing ringing current on a called extension, means associated with the transn'lission circuit at the called cxtension responsive to the operation of the last mentioned means for connecting the called extension with the transmission line of the calling extension, and signaling means as sociated with the keys of said trunk lines at the called extension operable during the period oi. such connection.

In testimony whereof, I have signed my name to this specification this 9th day of November, 1923.

Rani) s. BAILEY. 

